Do Releases of Hatchery Fishes into the Columbia River Basin Affect Growth and Survival of Wild Salmon?

Production of hatchery salmon has increased sharply since the 1970s, and adult hatchery returns now exceed wild salmon in many regions of the Pacific Rim, including the Columbia River.  Although many hatcheries were built on the premise of an unlimited capacity of freshwater and ocean habitats to support these fish, recent studies indicate that salmon compete for resources, leading to reduced growth and productivity.  In the Columbia River Basin, many wild salmon populations are depressed, implying that competition might be low.  However, significant competition may arise in response to reduced habitat capacity caused by watershed alterations and from numerous hatchery salmon.  This presentation reviews hatchery production and recent studies in the Basin that have been examined by the ISAB and ISRP.  Evidence indicates that competition with hatchery or non-native fishes reduces growth and/or productivity of wild salmon populations in freshwater and marine environments.  Furthermore, new information suggests that some supplementation projects, which are designed to rebuild wild salmon populations, show strong density-dependent responses, indicating that habitat capacity was exceeded even at low salmon population levels.  Thus, quality and quantity of habitat and prey production are key factors that must be considered when releasing large numbers of hatchery salmon.  In particular, fishery managers should consider these factors in association with supplementation projects designed to rebuild the wild salmon populations with hatchery salmon.